Feel a need, yes, for service (5)
I believe the answer is:
yearn
'feel a' is the definition.
I can't judge whether this definition defines the answer.
'yes for service' is the wordplay.
'yes' becomes 'yea' (I've seen this before).
'for' is a charade indicator (letters next to each other).
'service' becomes 'RN' (abbreviation for Royal Navy).
'yea'+'rn'='YEARN'
'need' is the link.
Can you help me to learn more?
(Other definitions for yearn that I've seen before include "wish" , "Hanker" , "Pant - pine" , "Long - pine" , "Have a great longing" .)